Methods for attaching a radiopaque marker to a scaffold

Abstract

A scaffold includes a radiopaque marker connected to a strut. The marker is retained within the strut by a head at one or both ends. The marker is attached to the strut by a process that includes forming a rivet from a radiopaque bead and attaching the rivet to the marker including deforming the rivet to enhance resistance to dislodgement during crimping or balloon expansion. The strut has a thickness of about 100 microns.

What is claimed is: 
     
       1. A method for making a medical device, comprising:
 using a polymer scaffold including a strut having a hole formed in the strut, wherein the strut has a thickness of between 80 and 120 microns measured between a first side of the strut and a second side of the strut and the strut comprises poly(L-lactide); and 
 using a radiopaque rivet marker having a head and a shank; and 
 placing the rivet into the hole so that the head is disposed on a first surface of the first side of the strut; and 
 swaging the rivet including making a deformed shank from the shank while the rivet sits in the hole; 
 wherein the head resists a first push-out force acting on the first surface by the head interfering with the first side of the hole; 
 wherein the deformed shank resists a second push-out force acting on a second surface of the second side of the strut by the deformed shank interfering with the second side of the hole; and 
 wherein before the swaging the hole is a cylindrical hole and after the swaging the hole is a tapered hole. 
 
     
     
       2. The method of  claim 1 , wherein
 the first surface is one of a luminal and abluminal surface of the scaffold and the second surface is the other one of the luminal and abluminal surface, 
 the strut has a width, and 
 a ratio of the width to the thickness is between 1.2 and 2.0. 
 
     
     
       3. The method of  claim 1 , wherein the swaging includes compressing the shank between a ram head and a mandrel, wherein a surface of the ram head has a higher coefficient of friction (Mu) than a Mu for a surface of the mandrel. 
     
     
       4. The method of  claim 1 ,
 wherein the shank has a shank length greater than the strut thickness, 
 wherein the shank is a cylinder, and 
 wherein the deformed shank is a frustum. 
 
     
     
       5. The method of  claim 4 ,
 wherein the head is disposed at a first opening of the first side of the hole and a base of the frustum is disposed at a second opening of the second side of the hole, and 
 wherein the swaging makes the second opening larger than the first opening. 
 
     
     
       6. The method of  claim 1 , wherein the deformed shank has a first end proximal of the head and a second end distal of the head, the first end is disposed at a first opening of the hole and the second end is disposed at a second opening of the hole,
 wherein prior to the swaging the first and second ends have the same diameter, and 
 wherein the swaging deforms the second opening and the second end such that the second end and second opening are larger than the first end and the first opening, respectively. 
 
     
     
       7. The method of  claim 1 , wherein the marker rivet has an undeformed length (L) before the swaging, a deformed length (L′) after the swaging, and L, L′ and the strut thickness (t) are related by
     t ×(1.2)≦ L≦t ×(1.8) and 1.2≦( L/t )≦1.8; and
 
     t ×(1.1)≦ L′≦t ×(1.5) and 1.1≦( L′/t )≦1.5.
 
 
     
     
       8. The method of  claim 1 , wherein the scaffold strut comprises poly(L-lactide). 
     
     
       9. The method of  claim 1 , wherein the scaffold is made from a polymer having a glass transition temperature (Tg), and wherein the scaffold is heated to a temperature of 0-20 degrees Celsius above its Tg after the rivet is deformed. 
     
     
       10. The method of  claim 1 , wherein the rivet is comprised of platinum, platinum/iridium alloy, iridium, tantalum, palladium, tungsten, niobium, zirconium, iron, zinc, magnesium, manganese or their alloys. 
     
     
       11. The method of  claim 1 , wherein the rivet is placed into the hole using a tool, and the tool comprises a vacuum tip configured for grabbing the head of the rivet and releasing the head therefrom by modifying a gas pressure at the tip. 
     
     
       12. The method of  claim 1 , wherein the first push-out force or the second push-out force is about an 80 gram-force. 
     
     
       13. A process for attaching a radiopaque material to a polymeric scaffold, comprising:
 using a die, deforming a spherical bead into a rivet having a head and shank, the bead comprising the radiopaque material; 
 attaching a tool to the rivet head, including creating a pressure difference at a tip of the tool to adhere the rivet head to the tool tip thereby, enabling the tool to lift and remove the rivet from the die and maintain an orientation of the rivet relative to the tip; 
 without removing the rivet from the tip of the tool and thereby maintaining an orientation of the shank relative to the tip:
 removing the rivet from the die, 
 transferring the rivet from the die to the scaffold using the tool, and 
 placing the shank through a hole of the scaffold, 
 wherein the rivet head rests on one of a luminal and abluminal surface of the strut and a tail of the shank extends out from the other of the luminal and abluminal surface; and 
 
 forming an interference fit between the rivet and hole including deforming the tail. 
 
     
     
       14. The method of  claim 13 , wherein the die comprises a plate having a hole and a counter bore. 
     
     
       15. The method of  claim 13 , wherein a push-out force for the shank from the hole is about an 80 gram-force. 
     
     
       16. The method of  claim 13 , wherein the scaffold has a strut thickness and a shank of the rivet has a length that is between 125% and 150% of the strut thickness. 
     
     
       17. The method of  claim 13 , wherein before forming the interference fit the hole is a cylindrical hole and after forming the interference fit the hole is a tapered hole. 
     
     
       18. The method of  claim 17 , wherein the shank formed from the die is cylindrical, and the forming an interference fit includes deforming the shank into a frustum. 
     
     
       19. The method of  claim 13 , wherein the hole is a polygonal hole or an elliptical hole. 
     
     
       20. A method for making a medical device, comprising:
 using a polymer scaffold including a strut having a hole formed in the strut, wherein the strut has a thickness of between 80 and 120 microns measured between a first side of the strut and a second side of the strut and the strut comprises poly(L-lactide); and 
 using a radiopaque rivet marker having a head and a shank; and 
 placing the rivet into the hole so that the head is disposed on a first side of the strut; and 
 swaging the rivet including making a deformed shank from the shank while the rivet sits in the hole; 
 wherein before swaging the hole is cylindrical and after swaging the hole is tapered, and 
 wherein before swaging the shank is cylindrical and after swaging the shank forms a frustum. 
 
     
     
       21. The method of  claim 20 , wherein the shank has a tail extending beyond a second side of the strut and outside the hole before swaging, and after swaging the tail is substantially within the hole.